The present invention relates to an image display device and, more particularly, to a head mounted display using a liquid crystal display with lenses for enlarging an image on a screen thereof.
This display device is used, for example, for viewing television and video programs, enjoining stereo images and virtual reality images, monitoring TV games and computer inputs and so on.
Recently, the head mounted displays (hereinafter referred to as HMD) have become actively studied with development of miniaturized liquid crystal displays (hereinafter referred to as LCD) device. As known, a conventional HMD device comprises a pair of enlarging lenses, a pair of field diaphragms, a pair of LCD and a pair of back lights. All components are mounted in a casing. A user can look at an enlarged image on a screen of the LCD device.
In the HMD device, all periphery of a main display image is covered with a black-colored field diaphragm to show effective display area of the LCD. Consequently, the user looks a floating screen in a black space.
The above-mentioned HMD device, however, may cause following problems:
The first problem is that the display image tires the eyes because the image has a large difference of brightness between its center portion and peripheral portion.
The second problem is that a viewer loses a usual atmosphere to be sensed when viewing a display screen in a room since his eyes is shut off all the surroundings.
To solve the above-mentioned problems, there has been proposed such a HMD device that presents a main liquid-crystal display image surrounded by an environmental image that may cause the user, for example, to feel as if he is viewing a movie on a TV screen in his room. This HMD device can attain the minimized difference of brightness between the LCD image and the environmental image and thereby does not tire the eyes of the user. This device can also offer such merits that the user gets a reference measure for recognizing a relative size of the screen, enjoys (a room atmosphere) and an increased feeling of his presence therein.
However, the HMD device with means for providing an environmental image may be not so effective as supposed because the environmental image can not vary.
For example, the brightness of a display screen image can not always be constant and may vary from time to time. Therefore, a large difference of brightness may be produced between the center portion image and the environmental image unless the brightness of the latter image varies correspondingly. In this instance, the image may tire the eyes, i.e., the first merit can not always be assured.
Furthermore, a user may become blind in a short time with his eyes taxed if brightness of a field-of-vision in the HMD device considerably differs from that of light in a room when of the field-of-vision in the HMD device when the user puts on and off the HMD device in the room.
Unless the environmental image varies as the center display image changes, total expression of the image may become tedious and can not cause the viewer to feel the sense of presence. The device can not realize the merit for increasing the ambient effect.
The ambience and impressiveness of an image are produced mainly by the effect of interactive audiovisual signals. The ambience can be lost when the image display device presents nothing but an environmental image.
Furthermore, it is very difficult for a viewer of the HMD to recognize the external circumstances.
Conventional HMD devices are designed for shutting off the outside vision and noises in order to get the viewer absorbed in the world filled with display screen images and accompanying speech and sound through a head phone. This may cause such a problem that the viewer can not sense what happened with or around him, for example, he is spoken to by somebody or a telephone is ringing.